Diversity receiver



Aug. 10, 1937. J. B. MOORE DIVERSITY RECEIVER Filed Feb. 20, 1936 6Sheets-Sheet 4 m wmbcm Q iv Us SR3 E INVENTOR. JOHN B. MOORE ATTORNEY.

Aug, 10, 1937. J. B. MOORE 2,089,568

DIVERSITY RECEIVER Filed Feb. 20, 1936 6 Sheets-Sheet 5 ZNVENTOR. Q v==JOHN B. MOORE BY fig wr'f/L ATTORNEY.

Aug. 10, 1937. J. B. MOORE 2,089,568

DIVERSITY RECEIVER Filed Feb. 20, 1956 6 Sheets-Sheet 6 gr/16mm? ym/P117S llllllll VIIvvvIvv INVENTOR. [EEO/805R {RECTIFIER JOHN B. MOOREATTORNEY.

Patented Aug. 1%, 1937 pairs ATEN QFFEQE DIVERSETY RECEIVER DelawareApplication February 20, 1936, Serial No. 64,801

6 Claims.

My present invention relates to the general improvement of diversityradio receivers.

Diversity receivers have proven especially successlul for the reductionof fadingan undesirable phenomenon experienced during the reception ofsignals transmitted on short radio waves. These receivers usually makeuse of a multiplicity of separated antennae whose currents either beforeor after rectification are combined to operate a single translatingdevice. However, diversity arrangements as heretofore known are, as faras I am aware, limited in flexibility.

Since flexibility is an extremely desirable characteristic in the tollcommunications field, the prime object of my present invention is toprovide va highly flexible diversity receiving system which may be usedfor telegraphic or telephonic signals, or which may be used to provideseparate signals of the telephonic or telegraphic type or which may beused to provide, simultaneously, separate signals some of Which resultfrom partial employment of full diversity receiving apparatus. Otherobjects, advantages and features of my present invention will becomeapparent as the more detailed description thereof proceeds.

Turning to the accompanying drawings, which are only illustrative of mypresent invention:

Figures 1 to 4 are block diagrams generally illustrative of my presentinvention;

Figure 5 schematically illustrates in somewhat greater detail the radiofrequency and intermediate frequency units of Figures 1 to 4 inelusive;

Figure 6 illustrates the signal control circuits of my present inventionwhich are utilized in a manner to be described more fully hereinafter;

Figure '7 is a Wiring diagram of an audio frequency amplifier which maybe used in connection with my present invention;

Figure 8 is a wiring diagram of a tone keying system useful inconnection with my present invention; and

Figure 9 illustrates a monitoring arrangement which may be used in mypresent diversity receiving system.

In the diversity receiving system which I am. about to describe ingreater detail, it has been found that three receivers have proven mostpracticable from the point of View of performance and economics.Additional receivers will, of course, add to the improvement inreception, but are not essential.

With the system herein disclosed, the three receivers may beutilizedz-to supply three separate telephone signals; to provide adiversity arrangement of three receivers; to supply a single telephonicsignal or a single telegraphic signal; or to connect two receivers oneither type of service, making the third receiver available for anothersignal. By a slight re-arrangement, three separate and diiferenttelegraphic signals may be received.

Figure 1 shows the general rack layout of the apparatus utilized in myimproved diversity receiving system. The radio frequency apparatus RFfor each receiver is placed on top. The radio frequency apparatus ofeach receiver is provided with separate tubes and circuits for each ofthree distinct frequency bands, the antenna transmission line plugs forwhich are indicated at Pl-i, i2, Pi-3, P2l, P2-2, P2-3, P3-l, P3--2 andP33. Beneath the radio frequency stages RF-i are placed, as indicated,the power control apparatus PC, audio frequency amplifier AF -lintermediate frequency apparatus IFi and diode detection apparatus DD-l.The apparatus beneath the radio frequency stages RF2 is quite similarwith the exception of the provision of signal control apparatus SC whichshall be described in greater detail hereinafter.

Beneath the radio frequency stages RF3 are mounted two tone keyers andoscillators TKO-l and TKO-Z. If desired, either of these tone keyers andoscillators may be replaced by an audio frequency amplifier such as AFIand AF-2. Various input, automatic gain control, and monitoring outputcircuits are provided, as indicated, and will be described in greaterdetail hereinafter.

Figures 2, 3, and 4 diagrammatically illustrate some of the combinationsobtainable with my improved diversity receiving apparatus, bymanipulation of the switches on the signal control panel SC of Figure 1.

In Figure 2 the three receivers are shown connected in full diversityfashion for either telephony or telegraphy. In Figure 3, two of thereceivers are combined to give diversity telephony or telegraphyreception and the other receiver is left free for either telegraphy ortelephony; and in Figure 4, the three receivers are arranged so as toproduce three separate signals.

Figure 5 shows in greater detail, although in block diagram form, theapparatus contained within the radio frequency units and intermediatefrequency units of Figure l. The antenna plugs Pll, PI2 and Pl3 may beconnected to antennae separately suited for different radio frequencybands such as, respectively, three to six megacycles, six to twelvemegacycles and twelve to twenty-four megacycles. These bands are chosensimply by way of illustration and are not to be considered in any way aslimiting the present invention. The output of block Pll is fedsuccessively through the antenna tuning stage ATL-I and radio frequencytuning stages RFTi i and RFTI2. These stages are pro- Vided with as manytubes, tuning circuits and individual controls or, if desired,unicontrolled controls as found desirable. The output of the radiofrequency tuning stage RFTi2 is fed to the tube detector stage TDi--lwhich is also supplied with oscillations from the local oscillator LO!I.All of this apparatus, including independent tubes in the amplifier,detector and oscillator stages are duplicated beneath the plugs Pl'2 andPl-3 with, of course, suitable adjustments in the circuits to make themsuitable for operation on the other frequency bands chosen. The radiofrequency filament switch RFS selectively energizes the filaments of alltubes under each plug. With the switch arms in their upper position, alltubes under plug Pi--l will be energized, thereby receiving signals towhich the three to six megacycle lband system is tuned. With the switcharms in the middle position, signals may be received on the channel orfrequency band to which the circuits under plug Pi 2 are adjusted, etc.As shown, the detectors TD|-I, TDI-2 and 'IDi3 have their outputsconnected in parallel and all channels are beat down by suitable tuningof the local oscillators, LOI-I, LOi2 and LOi-3 to a common intermediatefrequency such as three hundred kilocycles.

The apparatus of the unit RF! (Figure 5) is duplicated in the units RFZand RF3 of Figure 1, all of the outputs of which are beat down, as shownin Figure 5, to, for example, a common intermediate frequency such asthree hundred kilocycles.

Intermediate frequency energy is fed separately, as shown in Figure 5,to the intermediate frequency units IFE, IF2 and IF3 which are identicalin structure. Consequently, only unit IFI will be described in detail.

'Iihe intermediate frequency output of unit RF! is fed to a two stagetuned intermediate frequency amplifier TIFAi whose output in turn is fedto the IF detector IFDI. This heterodyne detector or frequency converterstage is supplied from the intermediate frequency local oscillator IFLO.

The output of the intermediate frequency detector IFD-I is adjusted tosome suitable value such as fifty kilocycles and fed through theintermediate frequency transformer IFTi to two intermediate frequencyamplifier units NFAI and WFA-l. Each of these fifty kilocycle amplifiersNFA-l and WFAE are suitably tuned and are provided with a suitablenumber of tubes to provide for desired amplification of the wavessupplied thereto. These amplifier stages, however, differ in thatamplifier NFA! passes a narrower band of frequencies and is adapted fortelegraphy as it tends to reduce noise level and eliminate interferencefrom: adjacent channels, whereas intermediate frequency amplifier WFA-Ihas a broader frequency characteris-, tic and is particularly suited fortelephony since it will tend to cause reproduction of the transmittedsignal with high fidelity. These amplifiers are selectively put intocircuit by the selective switch NWS whose switch arms when in theirupper position cause energization of the cathodes of the narrowintermediate frequency WFAI are fed to a common push-pull diode detectorDDI whose output is taken off at point X. Similarly, the outputs ofdiode detect ors DD2 and DD-3 of the intermediate frequency units IF-Zand IF--3 are taken from points Y and Z respectively. I

The connections X, Y, Z of Figure 5 are brought to the signal controlpanel SC of Figure l which is illustrated in greater detail in Figure 6.tector outputs of DDl, DD--2 and DD3 are connected respectively to thesignal indicators or milliammeters MAI, MA-Z and MA3. The outputconductor 2 of indicator MAI is connected to the switches !A and EB; theoutput conductor 4 of signal indicator MA-2 is connected as indicated tothe switches 2A and 2B,

and the output conductor 6 of MA-3 is connected to the switches 3A and33.

For a full diversity telegraphy connection, switches EB, 23 and 3B arethrown to their down As shown in Figure 6, the diode deposition so thatthe following contacts are closed:

iBi, IBZ, 2B5, 2B2, 3B! and 332. With these connections made, it will befound that the detected outputs of the three receivers are combined inthe conductor 8 which is fed to a tone keyer such as the tone keyerTKO.i of Figure 1 and which shall be described in greater detailhereinafter.

To indicate the combined output in indicator MA-4, contacts 4B! and 432are closed. Normally, contacts tBNl and liBNZ are closed. Automatic gaincontrol supply voltage for the radio frequency units RFI, RF2 and RF3 isbrought in from conductor ID and is fed back to the radio frequencyunits through conductors i2, 14 and [6 which lead to the grids of theradio frequency amplifier stages. RFTL-I, RFTi-2, RFT2l, RFT2--2, etc.of Figure 5.

To change the time constants on the various automatic gain controlcircuits, switches TCS and condensers TC, Figure 6, are provided.

For a full diversity telephony connection, switches IA, 2A and 3A arethrown to the up position so that the following contacts are closed:lAi, EAZ, 2Al, 2A2, SAi and 3A2, the switch iA being moved so thatcontacts 4A! and 5A2 are closed or in their normal position. To measurethe combined outputs, the contacts 5A3, 4A4 are closed, as a consequenceof which the combined output is made manifest in the signal indicator ormilliammeter M t-. The combined telephony signal will appear inconductor 26 and this is fed to a common audio frequency amplifier suchas AF- I or AF2 of Figure 1, which will be described in greater detailhereinafter. The automatic gain control with the full diversitytelephony connection is obtained from conductor 22 which, it will befound, is connected to the automatic gain control leads l2, M and i6leading to the radio frequency tubes of the radio frequency units RFl,RFZ and RF3 of Figure 1.

Now let it be supposed that it is desired to connect two receivers fordiversity telegraphy on a common signal and to have the other receiverconnected so as to receive a different telephonic signal. For example,let it be assumed that receiver 3 is to supply the telephonic signal andthat receivers l and 2 are to be combined in diversity fashion for atelegraphic signal. Contacts SM and 3A2 of switch 3A. are closed andwith the understanding that contacts 4M and 4A2 of switch 4A arenormally closed, it should be clear that on conductor 28 the audiofrequency signal will be impressed upon an audio frequency amplifiersuch as AFi of Figure 1. The automatic gain control voltage will bereturned for receiver 3 through lead 22, contacts SAI, now closed, andthence over conductor 56 to the radio frequency tubes of receiver 3. To

connect receivers i and 2 for telegraphic diversity on a common signal,switch contacts IBI and 132 of switch B3 are closed, as are contacts223i and 2152 of switch 23. The combined telegraphic signal is then fedout over conductor 8 to a suitable tone keyer such as TKO-2 of Figure 1and the automatic gain control voltage is brought in over conductor I8and fed to the radio frequency tubes of receivers I and 2 overconductors l2and l-i.

Attention is directed to the fact that in Figure 6 there is switching tothree audio frequency amplifier units and to one tone keyer unit. Ifdesired, the designation given in the brackets may be used so that theswitching of Figure 6 will correspond in every detail to the two audiofrequency amplifiers and two tone keyers and oscillators provided inFigure 1.

While it is preferable to have mechanically interlocked A and Bswitches, this interlocking is not essential since a reasonably skilledoperator will soon learn the various positions necessary to preventmix-up of signals.

Should it be desired that the three receivers operate on separatesignals; for example #1 on a telephony signal, #2 on a differenttelephony signal and #3 on a telegraphic signal, briefly the followingconnections may be made: Throw switch 1A to its up position so thatcontacts IA! and IA2 are closed; throw switch 2A to its down position sothat contacts 2A1 and 2A2 are closed; and finally, actuate switch 3B toits down position so that contacts 313! and 3132 are closed.

The wiring diagram of an audio frequency amplifier such as AFI or AFZ ofFigure 1 is given in Figure 7. Conductors such as 39 and 32 of Figure 6are connected directly to the terminals 3D, 32' of Figure 7. Automaticgain control voltage is provided with a suitable time constant ofoperation by the time constant circuit TC'I.

Audio frequency telephonic signal is fed to the two stage resistancecoupled amplifier AFRA and thence to a suitable output circuit, asindicated in Figure 7. In the case of diversity reception for telephonicsignals, the combined outputs of the diode detectors are, of course, fedinto terminal 39. The output of the audio frequency resistance coupledamplifier AFRA of Figure 7 may be utilized in a loudspeaker or fed tosuitable circuits for radio rebroadcasting.

A tone keyer oscillator such as TKOI of Figure 1 is illustrated ingreater detail in Figure 8. Referring to Figure 8, the contacts 8 and IDmay be connected respectively to the leads 8 and Ill of Figure 6. Thetelegraphic output from i, 2 or 3 of the diode detectors is fed in atthe contact 8' and in the presence of a signal current flow through thetube 40 is cut off. As a consequence, the plate lead 42 no longermaintains the grids of tubes 44 at a cut-off value, but

permits oscillations from a tone source 46 to be amplified by the tubes44 and eventually fed into a transmission line TL. This tone is fed tosome distant rectifier, for example, at some central receiving point,and the rectifier 50 operates a suitable recorder 54. In the absence ofsignal, current flow through tube 48 will cause such a high negativebias to be impressed upon the grids of tubes 44 that tone from source 46will not be fed into the transmission line IL.

The time control circuit T08 controls the time constant of the voltagefed back through contact ID" of Figure 8 and conductor l6 of Figure 6.

However, during code signaling, it is undesirable to have theamplification factor of the radio' frequency amplifiers high duringspacing periods, for this tends to raise the noise level. To remove theautomatic volume or gain control at such intervals, tube 60 and itsassociated circuits are provided. Tube 69 operates in such a way thatduring the period of no signal, the plate current flow reduces theamplification factor of the radio frequency amplifiers. In the presenceof signal, however, tube 6! becomes blocked and is rendered useless sothat only the rectified signal provides its own automatic gain controlvoltage over the conductor H3. The foregoing circuit is more fullydescribed and claimed in the copending application of R. L.Hollingsworth, Serial No. 732,565, filed June 27, 1934, and the circuitfor switching from the narrow band intermediate frequency amplifier tothe wide band intermediate frequency amplifier and vice versa of Figure5 is described and claimed more fully in my U. S. Patent 2,078,769,granted April 27, 1937 and in my copending application Serial No.699,318, filed November 23, 1933.

Figure 9 illustrates a suitable monitoring arrangement for the presentdiversity system. With the arrangement illustrated in Figure 9 it ispossible to monitor the audio frequency amplifiers and the variouskeying circuits. The monitor switches of Figure 9 are of the same typeas the diversity switches of Figure 6. Earphones are connected to themonitor jacks T9, 12 which, in turn, are connected to the monitoringswitches Ml, M2, M3, M4. The monitor switches are connected to theoutputs of the various units and are not connected in parallel to thediversity switches. For example, the leads marked AFI are connectedacross the output terminals marked "output of Figure 7. In the same way,the leads marked keyer are connected to the output terminals, so marked,of Figure 8. The leads marked IF are connected to the output of adetector which is supplied partially with the energy coming from suchintermediate frequency amplifiers as NFA--l and WFA-I of Figure 5 andwith energy from a local heterodyning oscillator. Such monitoring, whenusing leads marked IF, serves admirably well in check ing the tuning ofthe radio frequency oscillators, and for aural reception of slow speedtelegraphic signals. A rectifier type of volt meter RTV, shown in Figure9, is provided with an on-off switch OOS to indicate the strengths ofthe various monitored signals. This is used particularly for checkingand adjusting the strength of telephone or keyed tone signals suppliedto the lines leading to central offices or to broadcast control centers.

What I claim is:

1. Receiving apparatus comprising a plurality of antennas, a separateradio frequency amplifying and heterodyning unit connected to each antenna, rectifiers for separately rectifying the output of each of saidunits, a plurality of translating devices, and control switches forfeeding all of the rectified energy into one of said translating devicesand, at will, for separately feeding the rectified energy into differenttranslating devices, or for feeding the rectified outputs of a pair ofrectifiers into one translating device and the rectified output ofanother rectifier into a different translating device.

2. Apparatus asclaimed in claim 1, characterized by the fact that eachof said units includes Wide and narrow band circuits, and means to feedthe energy derived from the antennas selectively through said circuits.

3. Receiving apparatus comprising a plurality of antennas, a separateradio frequency amplifying unit connected to each antenna, rectifiersfor separately rectifying the output of each of said units, a pluralityof translating devices and a control switch for feeding all of therectified energy into one of said translating devices and, at Will, forseparately feeding the rectified energy into different translatingdevices, or for feeding the rectified outputs of a pair of rectifiersinto one translating device and the rectified output of anotherrectifier into a different translating device.

4. Apparatus as claimed in claim 3, characterized by the fact that eachof said units includes Wide and narrow band circuits, and means to feedthe energy derived from the antennas selectively through said circuits.

5. Receiving apparatus comprising a plurality of antennas, a separateradio frequency amplifying and heterodyning unit connected to eachantenna, rectifiers for separately rectifying the output of each of saidunits, a plurality of filter units of different band passcharacteristics and means operable at will for causing the energy fromone or more of said rectifying units to be fed through a selected one ofsaid filter units.

6. Apparatus according to claim 5 and having means for feeding to one ofsaid filter units the combined energies derived from different ones ofsaid antennas, While simultaneously feeding to another of said filterunits the energy derived solely from still another of said antennas.

JOHN B. MOORE.

